Most known examples of hydroxymethylglutaryl-CoA reductase are NADP-dependent (EC 1.1.1.34) from eukaryotes and archaea, involved in the biosynthesis of mevalonate from 3-hydroxy-3-methylglutaryl-CoA. This model, in contrast, is built from the two examples in completed genomes of sequences closely related to the degradative, NAD-dependent hydroxymethylglutaryl-CoA reductase of Pseudomonas mevalonii, a bacterium that can use mevalonate as its sole carbon source.